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Abstract:

An antenna includes a flexible sheet, a first coil electrode being formed
on a first main surface of the flexible sheet and a second coil electrode
being formed on a second main surface of the flexible sheet. Another end
portion of the first coil electrode and another end portion 32B of the
second coil electrode oppose each other with the flexible sheet there
between. One end portion of the first coil electrode opposes an electrode
pad, which has a smaller area than the one end portion, with a mounting
substrate there between. One end portion of the second coil electrode and
a central electrode oppose each other with the flexible sheet there
between, and the central electrode opposes an electrode pad, which has a
smaller area than the central electrode, with the mounting substrate
there between.

Claims:

1. An antenna comprising: a first coil electrode having a planar coil
shape and including a first end portion and a second end portion; a
second coil electrode that is spaced apart from the first coil electrode
by a predetermined distance, has a planar coil shape and includes a third
end portion and a fourth end portion; a first connection electrode and a
second connection electrode arranged to allow the second end portion of
the first coil electrode and the fourth end portion of the second coil
electrode to be connected to an external device; and a central electrode
that is arranged between the fourth end portion and the second connection
electrode; wherein the first coil electrode, the second coil electrode,
the first connection electrode, the second connection electrode and the
central electrode are arranged such that the first end portion and the
third end portion are capacitively coupled, the second end portion and
the first connection electrode are capacitively coupled, the fourth end
portion and the central electrode are capacitively coupled, and the
central electrode and the second connection electrode are capacitively
coupled; and a coupling capacitance between the first end portion and the
third end portion is larger than a coupling capacitance between the
second end portion and the first connection electrode and a coupling
capacitance between the fourth end portion and the central electrode is
larger than a coupling capacitance between the central electrode and the
second connection electrode.

2. The antenna according to claim 1, wherein the first coil electrode and
the second coil electrode have coil shapes in which, except for at end
portions thereof, are substantially not superposed with each other in a
direction perpendicular or substantially perpendicular to a plane
thereof.

3. The antenna according to claim 1, wherein the first coil electrode is
located on a first main surface of an insulating substrate that has a
predetermined thickness, and the second coil electrode is located on a
second main surface of the insulating substrate, the second main surface
opposing the first main surface.

4. The antenna according to claim 3, wherein the central electrode is
located on the first main surface.

5. The antenna according to claim 1, wherein the first connection
electrode and the second connection electrode and the second end portion
and the central electrode are arranged so as to oppose each other with an
insulating external-device-mounting substrate therebetween.

6. The antenna according to claim 5, wherein at least one of a coupling
electrode that opposes the first connection electrode and the second end
portion and a coupling electrode that opposes the second connection
electrode and the central electrode is located on a surface of the
external-device-mounting substrate on the second end portion and central
electrode side.

7. The antenna according to claim 1, wherein the first connection
electrode and the second connection electrode are located on the same
surface as the first coil electrode, the first connection electrode and
the second end portion are arranged on the same surface with a
predetermined gap therebetween such that there is a predetermined
coupling capacitance therebetween due to electromagnetic field coupling,
and the second connection electrode and the central electrode are
arranged on the same surface with a predetermined gap therebetween such
that there is a predetermined coupling capacitance therebetween due to
electromagnetic field coupling.

8. The antenna according to claim 1, wherein the first connection
electrode, the second connection electrode, the second end portion of the
first coil electrode and the central electrode are arranged such that at
least one of a condition that the first connection electrode has a
smaller area than the second end portion and a condition that the second
connection electrode has a smaller area than the central electrode is
satisfied.

9. An antenna module comprising: a wireless communication IC device; a
first coil electrode having a planar coil shape and including a first end
portion and a second end portion; a second coil electrode that is spaced
apart from the first coil electrode by a predetermined distance, has a
planar coil shape and includes a third end portion and a fourth end
portion; a first connection electrode and a second connection electrode
arranged to allow the second end portion of the first coil electrode and
the fourth end portion of the second coil electrode to be connected to
the wireless communication IC device; and a central electrode that is
arranged between the fourth end portion and the second connection
electrode; wherein the first coil electrode, the second coil electrode,
the first connection electrode, the second connection electrode and the
central electrode are arranged such that the first end portion and the
third end portion are capacitively coupled, the second end portion and
the first connection electrode are capacitively coupled, the fourth end
portion and the central electrode are capacitively coupled, and the
central electrode and the second connection electrode are capacitively
coupled; and a coupling capacitance between the first end portion and the
third end portion is larger than a coupling capacitance between the
second end portion and the first connection electrode, and wherein a
coupling capacitance between the fourth end portion and the central
electrode is larger than a coupling capacitance between the central
electrode and the second connection electrode.

10. An antenna module comprising: a wireless communication IC device that
includes a first mounting land electrode and a second mounting land
electrode; a first coil electrode having a planar coil shape and
including a first end portion and a second end portion; a second coil
electrode that is spaced apart from the first coil electrode by a
predetermined distance, has a planar coil shape and includes a third end
portion and a fourth end portion; and a central electrode that is
arranged between the fourth end portion and the second mounting land
electrode; wherein the first coil electrode, the second coil electrode
and the central electrode and the wireless communication IC device is
arranged with respect to the first coil electrode and the second coil
electrode such that the first end portion and the third end portion are
capacitively coupled, the second end portion and the first mounting land
electrode are capacitively coupled, the fourth end portion and the
central electrode are capacitively coupled and the central electrode and
the second mounting land electrode are capacitively coupled; a coupling
capacitance between the first end portion and the third end portion is
larger than a coupling capacitance between the second end portion and the
first mounting land electrode; and a coupling capacitance between the
fourth end portion and the central electrode is larger than a coupling
capacitance between the central electrode and the second mounting land
electrode.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to antennas and antenna modules that
are used in communication using electromagnetic field coupling such as
RFID communication.

[0003] 2. Description of the Related Art

[0004] Currently, short-range communication systems, in which a variety of
non-contact ICs are included, are widely used in a variety of fields.
This type of communication system includes a non-contact IC card, which
is equipped with, for example, a wireless communication IC, and a card
reader, and communication is performed by bringing the non-contact IC
card and the card reader within a predetermined distance from each other.
An antenna is needed to perform communication and the resonant frequency
of this antenna is set on the basis of the frequency of a communication
signal. Examples of such an antenna are described in Japanese Unexamined
Patent Application Publication No. 2001-84463 and Japanese Unexamined
Patent Application Publication No. 10-334203 and these antennas include a
coil electrode, which is wound to have a substantially planar shape, and
a structure that causes a capacitance to be generated, which, along with
the inductance of the coil electrode, is used to set the resonant
frequency.

[0005] For example, in Japanese Unexamined Patent Application Publication
No. 2001-84463, a coil electrode is provided that is wound in a
predetermined manner on each of a front surface side and a back surface
side of an insulating sheet. These coil electrodes are arranged so as to
oppose each other, whereby a desired capacitance is generated. In this
case, a large capacitance is obtained by making the width of the coil
electrodes large.

[0006] In addition, in Japanese Unexamined Patent Application Publication
No. 2001-84463, a structure is described in which a coil electrode and
one opposing electrode of the capacitor are formed on the front surface
side of the insulating sheet and the other opposing electrode of the
capacitor is formed on the back surface side of the insulating sheet. In
this structure, a conductive through hole is mechanically formed through
the insulating sheet in order to connect the back-surface-side opposing
electrode and a front-surface-side circuit pattern.

[0007] Furthermore, in Japanese Unexamined Patent Application Publication
No. 10-334203, a coil electrode is formed on the front surface side of an
insulating sheet and a coil electrode and an
electrostatic-capacitance-adjusting pattern, which is for causing a
capacitance to be generated, are formed on the back surface side of the
insulating sheet. Then, the capacitance is adjusted by adjusting the
shape (line length) of the electrostatic-capacitance-adjusting pattern.

[0008] However, with the structure of Japanese Unexamined Patent
Application Publication No. 2001-84463 described above, since the coil
electrode is formed to have a small number of turns and a large width,
although the capacitance is large, the inductance is very small.
Consequently, only a weak magnetic field can be radiated by the antenna
and the distance over which communication can be performed is short. This
is not suitable for data communication that requires a certain signal
level.

[0009] Furthermore, in the structure of the related art of Japanese
Unexamined Patent Application Publication No. 2001-84463 described above,
since the insulating sheet is subjected to mechanical punching in order
to physically bring the front-surface-side electrode pattern and the
back-surface-side electrode pattern into conductive contact with each
other, the manufacturing process is complex.

[0010] In addition, in the structure of Japanese Unexamined Patent
Application Publication No. 10-334203 described above, the
back-surface-side electrostatic-capacitance-adjusting pattern is formed
so as to be wound in the same direction as the front-surface-side coil
electrode, when viewed in plan, that is, along the direction of the
magnetic field at the surface of the antenna. Therefore, the
back-surface-side electrostatic-capacitance-adjusting pattern does not
contribute to the inductance of the antenna and the inductance of the
antenna only depends on the pattern of the front-surface-side coil
electrode. Consequently, an increase in the size of the structure due to,
for example, the number of windings of the front-surface-side coil
electrode being increased in order to increase the inductance so as to
increase the strength of the radiated magnetic field, is unavoidable.

[0011] In addition, in the case of such an antenna that includes a coil
electrode, the characteristics of the antenna are determined by the
inductance and capacitance of the coil electrode, which are determined by
the pattern of the coil electrode. However, it is not a simple matter to
design the antenna so that the inductance and the capacitance of the
antenna come to have predetermined values.

SUMMARY OF THE INVENTION

[0012] In view of these various issues, preferred embodiments of the
present invention provide an antenna with which a predetermined magnetic
field strength is obtained, that is simple and compact, and for which
designing of the characteristics thereof is simple. In addition, other
preferred embodiments of the present invention provide an antenna module
that includes antenna and has excellent communication characteristics.

[0013] An antenna according to a preferred embodiment of the present
invention includes a first coil electrode and a second coil electrode
that are arranged so as to oppose each other with a predetermined gap
therebetween. The first coil electrode preferably has a planar coil shape
and includes a first end portion and a second end portion. The second
coil electrode is spaced apart from the first coil electrode by a
predetermined distance, preferably has a planar coil shape, and includes
a third end portion and a fourth end portion.

[0014] In addition, this antenna includes a first connection electrode and
a second connection electrode arranged to allow the second end portion of
the first coil electrode and the fourth end portion of the second coil
electrode to be connected to an external device. This antenna includes a
central electrode that is arranged between the fourth end portion and the
second connection electrode.

[0015] In this antenna, the first coil electrode, the second coil
electrode, the first connection electrode, the second connection
electrode and the central electrode preferably have predetermined shapes
such that the first end portion and the third end portion are
capacitively coupled, the second end portion and the first connection
electrode are capacitively coupled, the fourth end portion and the
central electrode are capacitively coupled, and the central electrode and
the second connection electrode are capacitively coupled. In addition, in
this antenna, the coupling capacitance between the first end portion and
the third end portion is larger than the coupling capacitance between the
second end portion and the first connection electrode. Furthermore, in
this antenna, the coupling capacitance between the fourth end portion and
the central electrode is larger than the coupling capacitance between the
central electrode and the second connection electrode.

[0016] With this configuration, the capacitance of the antenna is more
greatly affected by the coupling capacitance between the second end
portion and the first connection electrode and the coupling capacitance
between the central electrode and the second connection electrode, than
by the coupling capacitance between the first end portion and the third
end portion and the coupling capacitance between the fourth end portion
and the central electrode. Therefore, by accurately forming and arranging
the portion at which the first connection electrode and the second end
portion are capacitively coupled with each other and the portion at which
the second connection electrode and the central electrode are
capacitively coupled with each other, which are structures for allowing
connection to an external device, a degree of freedom can be provided to
the structures of other components of the antenna. Thus, an antenna can
be provided that has a simple design and stable characteristics.

[0017] In addition, in an antenna according to a preferred embodiment of
the present invention, the first coil electrode and the second coil
electrode preferably have coil shapes in which, except for at end
portions thereof, the electrodes are substantially not superposed with
each other in a direction perpendicular or substantially perpendicular to
a plane thereof.

[0018] With this configuration, the first coil electrode and the second
coil electrode can be caused to be capacitively coupled with each other
mainly at the respective end portions thereof.

[0019] In addition, in an antenna according to a preferred embodiment of
the present invention, the first coil electrode can be located on a first
main surface of an insulating substrate having a predetermined thickness.
The second coil electrode can be located on a second main surface of the
insulating substrate, the second main surface opposing the first main
surface.

[0020] With this configuration, the specific structures of the first coil
electrode and the second coil electrode are provided. Thus, by arranging
the first coil electrode and the second coil electrode so as to oppose
respective main surfaces of the insulating substrate, the above-described
structure can be easily realized.

[0021] In addition, in an antenna according to a preferred embodiment of
the present invention, the central electrode can be located on the first
main surface.

[0022] With this configuration, the specific structure of the central
electrode is described. Thus, if the first coil electrode and the central
electrode are located on the same first main surface, the structure is
simplified and it becomes easy to set the coupling capacitances between
the first coil electrode and the second coil electrode and the first
connection electrode and the second connection electrode.

[0023] In addition, in an antenna according to a preferred embodiment of
the present invention, the first connection electrode and the second
connection electrode and the second end portion and the central electrode
may be arranged so as to oppose each other with an insulating
external-device-mounting substrate therebetween.

[0024] With this configuration, a specific structure is described that
provides the positional relationship between the first connection
electrode and the second connection electrode and the second end portion
and the central electrode.

[0025] In addition, in an antenna according to a preferred embodiment of
the present invention, at least one of a coupling electrode that opposes
the first connection electrode and the second end portion and a coupling
electrode that opposes the second connection electrode and the central
electrode may be located on a surface of the external-device-mounting
substrate on the side of the second end portion and the central
electrode.

[0026] With this configuration, by utilizing coupling electrodes, coupling
capacitances, which are generated by arranging the first connection
electrode and the second connection electrode as constituent elements,
can be realized more reliably than by directly mounting an external
device on the insulating substrate.

[0027] In addition, in an antenna according to a preferred embodiment of
the present invention, the first connection electrode and the second
connection electrode may be located on the same surface as the first coil
electrode. In this antenna, the first connection electrode and the second
end portion may be arranged on the same surface with a predetermined gap
therebetween such that there is a predetermined coupling capacitance due
to electromagnetic field coupling. In this antenna, the second connection
electrode and the central electrode may be arranged on the same surface
with a predetermined gap therebetween such that there is a predetermined
coupling capacitance due to electromagnetic field coupling.

[0028] With this configuration, a case is illustrated in which the first
connection electrode and the second connection electrode are located on
the same surface as the first coil electrode. Also with this
configuration, the same functional effect is obtained as in the
above-described case in which an external-device-mounting substrate is
used. Furthermore, with this configuration, there is no need for use of
an external-device-mounting substrate and a simpler configuration can be
realized.

[0029] In addition, in an antenna according to a preferred embodiment of
the present invention, the first connection electrode, the second
connection electrode, the second end portion of the first coil electrode
and the central electrode may have shapes such that at least one of a
condition that the first connection electrode has a smaller area than
that of the second end portion and a condition that the second connection
electrode has a smaller area than that of the central electrode is
satisfied.

[0030] With this configuration, the above-described relationship between
the coupling capacitances and the structure for more specifically
realizing this are described. Thus, the areas of the first connection
electrode and the second connection electrode are made small, whereby the
coupling capacitances obtained by arranging the first connection
electrode and the second connection electrode as constituent elements can
be easily made small.

[0031] In addition, other preferred embodiments of the present invention
relate to an antenna module that includes a wireless communication IC
device. The antenna module includes a first coil electrode and a second
coil electrode. The first coil electrode preferably has a planar coil
shape and includes a first end portion and a second end portion. The
second coil electrode is spaced apart from the first coil electrode by a
predetermined distance, preferably has a planar coil shape, and includes
a third end portion and a fourth end portion. In addition, this antenna
module includes a first connection electrode and a second connection
electrode arranged to allow the second end portion of the first coil
electrode and the fourth end portion of the second coil electrode to be
connected to the wireless communication IC device. This antenna module
includes a central electrode that is arranged between the fourth end
portion and the second connection electrode. In this antenna module, the
first coil electrode, the second coil electrode, the first connection
electrode, the second connection electrode and the central electrode
preferably have predetermined shapes such that the first end portion and
the third end portion are capacitively coupled, the second end portion
and the first connection electrode are capacitively coupled, the fourth
end portion and the central electrode are capacitively coupled, and the
central electrode and the second connection electrode are capacitively
coupled. In addition, in this antenna module, the coupling capacitance
between the first end portion and the third end portion is larger than
the coupling capacitance between the second end portion and the first
connection electrode. Furthermore, in this antenna module, the coupling
capacitance between the fourth end portion and the central electrode is
larger than the coupling capacitance between the central electrode and
the second connection electrode.

[0032] With this configuration, description has been given of an antenna
module that includes the above-described antenna structure and in which a
wireless communication IC is mounted.

[0033] In addition, preferred embodiments of the present invention relate
to an antenna module that includes a wireless communication IC device.
The wireless communication IC device includes a first mounting land
electrode and a second mounting land electrode. In addition, the antenna
module includes a first coil electrode and a second coil electrode. The
first coil electrode preferably has a planar coil shape and includes a
first end portion and a second end portion. The second coil electrode is
spaced apart from the first coil electrode by a predetermined distance,
preferably has a planar coil shape, and includes a third end portion and
a fourth end portion. In addition, this antenna module includes a central
electrode that is arranged between the fourth end portion and the second
mounting land electrode. In the antenna module, the first coil electrode,
the second coil electrode and the central electrode preferably have
predetermined shapes and the wireless communication IC device is arranged
with respect to the first coil electrode and the second coil electrode
such that the first end portion and the third end portion are
capacitively coupled, the second end portion and the first mounting land
electrode are capacitively coupled, the fourth end portion and the
central electrode are capacitively coupled and the central electrode and
the second mounting land electrode are capacitively coupled. In addition,
in this antenna module, the coupling capacitance between the first end
portion and the third end portion is larger than the coupling capacitance
between the second end portion and the first mounting land electrode. In
addition, in this antenna module, the coupling capacitance between the
fourth end portion and the central electrode is larger than the coupling
capacitance between the central electrode and the second mounting land
electrode.

[0034] With this configuration, description has been made of a
configuration in a case where the above-described first connection
electrode and second connection electrode are not included and the first
mounting land electrode and the second mounting land electrode for the
wireless communication IC are used instead of the first connection
electrode and the second connection electrode. Also with this
configuration, an antenna module having stable characteristics is
realized.

[0035] According to various preferred embodiments of the present
invention, an antenna is provided that generates a stronger magnetic
field than in the related art, is simple and compact and for which the
designing of characteristics thereof is simple. In addition, an antenna
module is provided that includes the antenna and has excellent
communication characteristics.

[0036] The above and other elements, features, steps, characteristics and
advantages of the present invention will become more apparent from the
following detailed description of the preferred embodiments with
reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 is an exploded perspective view illustrating the
configuration of an antenna module 100 according to a first preferred
embodiment of the present invention.

[0038] FIGS. 2A and 2B are a plan view and a side view of the antenna
module 100 according to the first preferred embodiment of the present
invention.

[0039]FIG. 3 illustrates the antenna module 100 according to the first
preferred embodiment of the present invention as an equivalent circuit
seen from the side.

[0040]FIG. 4 is a side view of an antenna module 100A according to a
second preferred embodiment of the present invention.

[0041]FIG. 5 illustrates the antenna module 100A according to the second
preferred embodiment of the present invention as an equivalent circuit
seen from the side.

[0042]FIG. 6 is a side view of an antenna module 100B according to a
third preferred embodiment of the present invention.

[0043]FIG. 7 is an exploded perspective view illustrating the
configuration of an antenna module 100C according to a fourth preferred
embodiment of the present invention.

[0044] FIGS. 8A and 8B are a plan view and a side view of the antenna
module 100C according to the fourth preferred embodiment.

[0045]FIG. 9 is an exploded perspective view illustrating the
configuration of an antenna module 100D according to a fifth preferred
embodiment of the present invention.

[0046]FIG. 10 is a side view of the antenna module 100D according to a
fifth preferred embodiment of the present invention.

[0047] FIGS. 11A and 11B are plan views illustrating another example of
formation of a first coil electrode and a second coil electrode.

[0049] An antenna and an antenna module according to a first preferred
embodiment of the present invention will now be described with reference
to the drawings.

[0050]FIG. 1 is an exploded perspective view illustrating the
configuration of an antenna module 100 according to this preferred
embodiment. FIG. 2A is a plan view seen from a first main surface 12 side
of the antenna module 100 and FIG. 2B is a side view of the antenna
module 100.

[0051] The antenna module 100 includes an antenna 1 and a wireless
communication IC 80. The antenna 1 includes a thin-film flexible sheet
10, which is a flat board preferably made of an insulating material such
as a resin, and a mounting substrate 15 for the wireless communication IC
80.

[0052] A first coil electrode 21 is located on the first main surface 12
of the flexible sheet 10 and a second coil electrode 31 is located on a
second main surface 13, which opposes the first main surface 12, of the
flexible sheet 10. The first coil electrode 21 and the second coil
electrode 31 preferably are line-shaped electrodes, which are preferably
made of a metal thin film or the like preferably having a coil shape, and
are attached to the flexible sheet 10 with an adhesive or the like.

[0053] The first coil electrode 21 includes one end portion 22A at the
outermost periphery thereof (corresponding to a "second end portion"
according to a preferred embodiment of the present invention) and another
end portion 22B at the innermost periphery thereof (corresponding to a
"first end portion" according to a preferred embodiment of the present
invention). The first coil electrode 21 has a structure in which a
line-shaped electrode continuously extends from the one end portion 22A
at the outermost periphery to the other end portion 22B at the innermost
periphery by being wound sequentially counterclockwise toward the inner
peripheral side, when the flexible sheet 10 is viewed from the first main
surface 12 side.

[0054] The second coil electrode 31 includes one end portion 32A at the
outermost periphery thereof (corresponding to a "fourth end portion"
according to a preferred embodiment of the present invention) and another
end portion 32B at the innermost periphery thereof (corresponding to a
"third end portion" according to a preferred embodiment of the present
invention.). The second coil electrode 31 has a structure in which a
line-shaped electrode continuously extends from the other end portion 32B
at the innermost periphery to the one end portion 32A at the outermost
periphery by being sequentially wound clockwise toward the outer
peripheral side, when the flexible sheet 10 is viewed from the second
main surface 13 side. In other words, the second coil electrode 31 has a
shape in which it is wound in the opposite direction to the first coil
electrode 21.

[0055] Then, with this configuration, the first coil electrode 21 and the
second coil electrode 31 have a shape in which they are continuously
wound in the same direction when the second main surface 13 is viewed
from the same direction, for example, from the first main surface 12.
Thus, the directions in which currents flow through the first coil
electrode 21 and the second coil electrode 31 are the same and the
direction of the magnetic field generated by the first coil electrode 21
and the direction of the magnetic field generated by the second coil
electrode 31 are the same. As a result, these magnetic fields act so as
to be added together and the magnetic field, serving as the antenna
(magnetic field whose axis extends in a direction perpendicular or
substantially perpendicular to the main surface) becomes stronger. In
other words, the first coil electrode 21 and the second coil electrode 31
function as a single coil whose winding direction does not change midway
therealong, is continuous and has a greater number of turns.

[0056] In this case, without carrying out mechanical connection processing
such as forming holes in the flexible sheet 10, by simply forming end
portions of the first coil electrode 21 and the second coil electrode 31
so that they oppose each other, the first coil electrode 21 and the
second coil electrode 31 can be connected in an alternating manner and
therefore a resonance type antenna can be formed by using a simple method
and so as to have a simple structure.

[0057] The number of turns of the first coil electrode 21 and a length
from a position in the center of the plane of the first coil electrode 21
to the group of electrodes are set on the basis of the inductance L21
(refer to FIG. 3), which is to be realized using the first coil electrode
21. Furthermore, the number of turns of the second coil electrode 31 and
a length from a position in the center of the plane of the second coil
electrode 31 to the group of electrodes are set on the basis of the
inductance L31 (refer to FIG. 3), which is to be realized using the
second coil electrode 31.

[0058] The outermost peripheral end portion 22A and the innermost
peripheral end portion 22B of the first coil electrode 21 preferably have
a substantially square shape having a width that is larger than that of
the wound line-shaped electrode portion. The outermost peripheral end
portion 32A and the innermost peripheral end portion 32B of the second
coil electrode 31 also have a substantially square shape having a width
that is larger than that of the wound line-shaped electrode portions.

[0059] The first coil electrode 21 and the second coil electrode 31 have
shapes in which the innermost peripheral end portions 22B and 32B are
superposed with each other in plan view. In this way, the first coil
electrode 21 and the second coil electrode 31 are connected to each other
in an alternating manner. In addition, a capacitor can be provided that
has a large opposing area and a comparatively large value of capacitance
C23B (refer to FIG. 3) in accordance with the opposing area of the other
end portions 22B and 32B and the thickness and dielectric constant of the
flexible sheet 10.

[0060] The first coil electrode 21 and the second coil electrode 31, as
illustrated in FIG. 2A, preferably have shapes such that, except for at
the innermost peripheral end portions thereof, the coil electrodes are
almost entirely not superposed with each other along line-shaped
electrode portions thereof.

[0061] A substantially square-shaped central electrode 22C is disposed on
the first main surface of the flexible sheet at a position that is
separated from the outermost peripheral end portion 22A of the first coil
electrode 21 by a predetermined distance. Specifically, the central
electrode 22C is disposed so as to be superposed with the outermost
peripheral end portion 32A of the second coil electrode 31 in plan view.
The central electrode 22C also preferably has substantially the same area
as the outermost peripheral end portions 22A and 32A and the innermost
peripheral end portions 22B and 32B. In this way, a capacitor preferably
includes the outermost peripheral end portion 32A of the second coil
electrode 31, the central electrode 22C and the flexible sheet 10, the
capacitor having a large opposing area and a comparatively large
capacitance C23A.

[0062] The mounting substrate 15 includes an insulator layer that is
substantially square-shaped when viewed in plan and preferably includes
an area that encompasses the outermost peripheral end portion 22A of the
first coil electrode 21 and the central electrode 22C and in which the
wireless communication IC 80 can be mounted.

[0063] A plurality of electrode pads (for example, four in FIG. 1 and
FIGS. 2A and 2B) including electrode pads 151A (corresponding to a "first
connection electrode" according to a preferred embodiment of the present
invention) and 151B (corresponding to a "second connection electrode"
according to a preferred embodiment of the present invention) are formed
on one surface of the mounting substrate 15. The wireless communication
IC 80 is mounted using these electrode pads. The electrode pads 151A and
151B have an area that is substantially the same as that of mounting
lands that are located on the wireless communication IC 80. The
arrangement interval of the electrode pads 151A and 151B is substantially
the same as the arrangement interval of the outermost peripheral end
portion 22A and the central electrode 22C.

[0064] The mounting substrate 15 is disposed on the first main surface 12
side of the flexible sheet 10 such that the electrode pad 151A is
superposed with the outermost peripheral end portion 22A and the
electrode pad 151B is superposed with the central electrode 22C. At this
time, the mounting substrate 15 is attached to the flexible sheet 10 by
using, for example, an insulating adhesive agent or adhesive sheet. With
this configuration, a capacitor is preferably defined by the electrode
pad 151A, the outermost peripheral end portion 22A and the mounting
substrate 15, the capacitor having a small opposing area and a small
capacitance C25A. In addition, a capacitor is preferably defined by the
electrode pad 151B, the central electrode 22C and the mounting substrate
15, the capacitor having a small opposing area and a small capacitance
C25B.

[0065] With this configuration, the antenna module 100 of the present
preferred embodiment has the circuit configuration illustrated in FIG. 3.
FIG. 3 illustrates the antenna module 100 of the present preferred
embodiment as an equivalent circuit seen from the side.

[0066] As illustrated in FIG. 3, a capacitor (capacitance C25A) defined by
the electrode pad 151A and the outermost peripheral end portion 22A, an
inductor (inductance L21) defined by the first coil electrode 21 and a
capacitor (capacitance C23B) defined by the innermost peripheral end
portions 22B and 32B, are connected in series with one another between
one terminal of the wireless communication IC 80 on the electrode pad
151A side and an inductor (inductance L31) defined by the second coil
electrode 31.

[0067] Here, the capacitance C25A defined by the electrode pad 151A and
the outermost peripheral end portion 22A is smaller than the capacitance
C23B defined by the innermost peripheral end portions 22B and 32B.
Therefore, the combined capacitance obtained using the formula to combine
capacitances connected in series is strongly affected by the small
capacitance C25A but is weakly affected by the large capacitance C23B.
Therefore, provided that the capacitance C25A is stable, the combined
capacitance is stable even if the capacitance C23B varies.

[0068] In addition, a capacitor (capacitance C25B) defined by the
electrode pad 151B and the central electrode 22C and a capacitor
(capacitance C23A) defined by the central electrode 22C and the outermost
peripheral end portion 32A are connected in series with each other
between another terminal of the wireless communication IC 80 on the
electrode pad 151B side and the inductor (inductance L31) defined by the
second coil electrode 31.

[0069] Here, the capacitance C25B defined by the electrode pad 151B and
the central electrode 22C is smaller than the capacitance C23A defined by
the central electrode 22C and the outermost peripheral end portion 32A.
Therefore, the combined capacitance obtained using the formula to combine
capacitances connected in series is strongly affected by the small
capacitance C25B but is weakly affected by the large capacitance C23A.
Therefore, provided that the capacitance C25B is stable, the combined
capacitance is stable even if the capacitance C23A varies.

[0070] Thus, with the configuration of this preferred embodiment, the
capacitance of the resonant circuit is substantially determined by the
capacitance C25A defined by the electrode pad 151A and the outermost
peripheral end portion 22A and the capacitance C25B defined by the
electrode pad 151B and the central electrode 22C arranged on the both
surfaces of the mounting substrate 15.

[0071] Here, the electrode pads 151A and 151B have smaller areas than the
outermost peripheral end portion 22A and the central electrode 22C, in
other words, the outermost peripheral end portion 22A and the central
electrode 22C have larger areas than the electrode pads 151A and 151B,
and therefore when the mounting substrate 15 is arranged on the flexible
sheet 10, the electrode pads 151A and 151B and the outermost peripheral
end portion 22A and the central electrode 22C can be arranged so as to
oppose each other with high certainty even if there are some variations
in position. Thus, the capacitances C25A and C25B, which depend on the
electrode pads 151A and 151B, do not vary.

[0072] Therefore, even if there are variations in formation of the antenna
1, the capacitances C25A and C25B will not vary and therefore the
resonant frequency of the resonant circuit of the antenna 1 is negligibly
affected. Therefore, with this antenna structure, an antenna module
having stable communication characteristics is provided.

[0073] In addition, in the configuration of this preferred embodiment, the
wireless communication IC 80 is mounted on the electrode pads 151A and
151B, which have a small area, of the mounting substrate 15 and therefore
the accuracy and speed with which the wireless communication IC 80 is
mounted can be improved. Thus, the manufacturing yield and the
manufacturing speed for the antenna module 100 can also be improved.

[0074] In the above description, the capacitances C25A and C25B were only
described as being smaller than the capacitances C23A and C23B, but
specifically the capacitances C23A and C23B are on the order of about 100
pF, for example, and the capacitances C25A and C25B are on the order of
about 20 pF, for example.

[0075] If the capacitances are set in this way and the above-described
configuration and manufacturing method are used, high accuracy can be
realized comparatively easily and the capacitances C25A and C25B can be
realized within a range of about 20 pF±1.0% to 2.0%, for example.

[0076] The characteristics of the antenna can be set to be within a range
of variability of, for example, about 13.56 MHz±200 kHz by setting the
capacitances in the above-described way.

[0077] Thus, by using the configuration of this preferred embodiment, an
antenna that has desired high-accuracy characteristics can be easily
realized.

[0078] The set values of these capacitances are examples and the
difference between the capacitances C25A and C25B and the capacitances
C23A and C23B may be made larger on the basis of the desired
characteristics of the antenna.

[0079] Furthermore, in the above description, an example was described in
which the capacitances C25A and C25B are made small by making the areas
of the electrode pads 151A and 151B small, but the capacitances C25A and
C25B may be instead made small by changing the material of the mounting
substrate 15 or by increasing the thickness of the mounting substrate 15.

[0080] Next, an antenna and an antenna module according to a second
preferred embodiment according to the present invention will be described
with reference to the drawings. FIG. 4 is a side view of an antenna
module 100A according to the second preferred embodiment according to the
present invention.

[0081] The antenna module 100A (antenna 1A), in contrast to the antenna
module 100 (antenna 1) described in the first preferred embodiment, has a
configuration in which mounting electrodes 152A and 152B are arranged on
the flexible sheet 10 side of the mounting substrate 15.

[0082] The mounting electrode 152A is preferably arranged so as to be
superposed with the electrode pad 151A when viewed in plan and preferably
has substantially the same shape as the outermost peripheral end portion
22A. The mounting electrode 152B is preferably arranged so as to be
superposed with the electrode pad 151B when viewed in plan and preferably
has substantially the same shape as the central electrode 22C.

[0083] The mounting substrate 15 is disposed on the flexible sheet 10 such
that the mounting electrode 152A and the outermost peripheral end portion
22A are superposed with each other and that the mounting electrode 152B
and the central electrode 22C are superposed with each other. The
mounting substrate 15 and the flexible sheet 10 are attached to each
other using, for example, an insulating adhesive sheet 16.

[0084] With this configuration, the antenna module 100A of the present
preferred embodiment has the circuit configuration illustrated in FIG. 5.
FIG. 5 illustrates the antenna module 100A of the present preferred
embodiment as an equivalent circuit seen from the side.

[0085] As illustrated in FIG. 5, a capacitor (capacitance C25A) defined by
the electrode pad 151A and the mounting electrode 152A, a capacitor
(capacitance C55A) defined by the mounting electrode 152A and the
outermost peripheral end portion 22A, an inductor (inductance L21)
defined by the first coil electrode 21 and a capacitor (capacitance C23B)
defined by the innermost peripheral end portions 22B and 32B, are
connected in series with one another between one terminal of the wireless
communication IC 80 on the electrode pad 151A side and an inductor
(inductance L31) defined by the second coil electrode 31.

[0086] Here, the capacitance C25A defined by the electrode pad 151A and
the mounting electrode 152A is smaller than the capacitance C23B defined
by the innermost peripheral end portions 22B and 32B. In addition, the
capacitance C55A defined by the mounting electrode 152A and the outermost
peripheral end portion 22A is a capacitance that is substantially the
same as the capacitance C23B. Therefore, the combined capacitance
obtained using the formula to combine capacitances connected in series is
strongly affected by the small capacitance C25A but is weakly affected by
the large capacitances C55A and C23B. Therefore, provided that the
capacitance C25A is stable, the combined capacitance will be stable even
if the capacitances C55A and C23B vary.

[0087] In addition, a capacitor (capacitance C25B) defined by the
electrode pad 151B and the mounting electrode 152B, a capacitor
(capacitance C55B) defined by the mounting electrode 152B and the central
electrode 22C, and a capacitor (capacitance C23A) defined by the central
electrode 22C and the outermost peripheral end portion 32A are connected
in series with one another between another terminal of the wireless
communication IC 80 on the electrode pad 151B side and the inductor
(inductance L31) defined by the second coil electrode 31.

[0088] Here, the capacitance C25B defined by the electrode pad 151B and
the mounting electrode 152B is smaller than the capacitance C23A defined
by the central electrode 22C and the outermost peripheral end portion
32A. In addition, the capacitance C55B defined by the mounting electrode
152B and the central electrode 22C is a capacitance that is substantially
the same as the capacitance C23A. Therefore, the combined capacitance
obtained using the formula to combine capacitances connected in series is
strongly affected by the small capacitance C25B but is weakly affected by
the large capacitances C55B and C23A. Therefore, provided that the
capacitance C25B is stable, the combined capacitance will be stable even
if the capacitances C55B and C23A vary.

[0089] Thus, with the configuration of this preferred embodiment, the
capacitance of the resonant circuit is substantially determined by the
capacitance C25A defined by the electrode pad 151A and the mounting
electrode 152A and the capacitance C25B defined by the electrode pad 151B
and the mounting electrode 152B arranged on the both surfaces of the
mounting substrate 15.

[0090] Therefore, similarly to the first preferred embodiment, even if
there are variations in the formation of the antenna 1A, the capacitances
C25A and C25B will not vary and therefore the resonant frequency of the
resonant circuit of the antenna 1A and the antenna module 100A will be
negligibly affected and an antenna module having stable communication
characteristics is provided.

[0091] Furthermore, with the configuration of this preferred embodiment,
the electrode pads 151A and 151B and the mounting electrodes 152A and
152B are preferably formed at the time of forming the mounting substrate
15 and therefore these electrodes can be arranged to oppose one another
with high accuracy. Thus, the capacitances C25A and C25B can be set with
high accuracy and the antenna and antenna module can be formed with
greater stability. In this preferred embodiment, an example was described
in which the mounting electrodes 152A and 152B preferably have
substantially the same area as the central electrode 22C and the
outermost peripheral end portion 22A, but so long as the mounting
electrode 152A and 152B have larger areas than the electrode pads 151A
and 151B, the configuration of this preferred embodiment can be adopted.
In addition, in this preferred embodiment, an example was described in
which two mounting electrodes are arranged to oppose two corresponding
electrode pads, but instead only a single mounting electrode that opposes
a single electrode pad may be provided.

[0092] Next, an antenna module according to a third preferred embodiment
of the present invention will be described with reference to the
drawings. FIG. 6 is a side view of an antenna 1B and an antenna module
100B according to this preferred embodiment of the present invention. As
illustrated in FIG. 6, in contrast to the antenna 1 and the antenna
module 100 described in the first preferred embodiment of the present
invention, the mounting substrate 15 is omitted from the antenna 1B and
the antenna module 100B of this preferred embodiment of the present
invention.

[0093] In the antenna module 100B, mounting lands 81A and 81B located on
the wireless communication IC 80 are arranged so as to oppose the
outermost peripheral end portion 22A and the central electrode 22C with
an insulating adhesive layer 17 therebetween.

[0094] Also with this configuration, as with the first preferred
embodiment, an antenna module can be provided that is not affected by
variations in formation of the antenna 1B and has stable communication
characteristics.

[0095] Next, an antenna module according to a fourth preferred embodiment
of the present invention will be described with reference to the
drawings. FIG. 7 is an exploded perspective view illustrating the
configuration of an antenna module 100C according to this preferred
embodiment of the present invention. FIG. 8A and FIG. 8B are a plan view
and a side view of the antenna module 100C according to this preferred
embodiment of the present invention.

[0096] The antenna module 100C includes an antenna 1C and the wireless
communication IC 80.

[0097] The antenna 1C has a structure that preferably is basically the
same as that of the antenna 1 described in the first preferred embodiment
of the present invention and a first coil electrode 21C preferably has a
coil shape on a first main surface of an insulating flexible sheet 10C
and a second coil electrode 31C preferably has a coil shape on a second
main surface of the flexible sheet 10C. The first coil electrode 21C has
a shape in which it is sequentially wound toward the inside in the
counterclockwise direction from the outermost peripheral end portion 22A
to the innermost peripheral end portion 22B, when viewed from the first
main surface side. The second coil electrode 31C has a shape in which it
is sequentially wound toward the outside in the clockwise direction from
the innermost peripheral end portion 32B to the outermost peripheral end
portion 32A, when viewed from the second main surface side.

[0098] The outermost peripheral end portion 22A and the innermost
peripheral end portion 22B of the first coil electrode 21C have shapes
having a width that is larger than that of the wound line-shaped
electrode portion. The outermost peripheral end portion 32A and the
innermost peripheral end portion 32B of the second coil electrode 31C
also have shapes having a width that is larger than that of the wound
line-shaped electrode portion.

[0099] The first coil electrode 21C and the second coil electrode 31C have
shapes such that the innermost peripheral end portions 22B and 32B are
superposed with each other in plan view. In this way, a capacitor is
defined by the innermost peripheral end portions 22B and 32B of the first
coil electrode 21C and the second coil electrode 31C and the flexible
sheet 10C, the capacitor having a large opposing area and a comparatively
large capacitance.

[0100] The first coil electrode 21C and the second coil electrode 31C, as
illustrated in FIG. 8A, are arranged so as to have shapes such that,
except for at the outermost peripheral end portions and the innermost
peripheral end portions thereof, the electrodes are almost entirely not
superposed with each other along the line-shaped electrode portions
thereof.

[0101] The central electrode 22C, which has substantially the same area as
the outermost peripheral end portion 22A, is arranged at a position
spaced apart from the outermost peripheral end portion 22A of the first
coil electrode 21C by a predetermined distance on the first main surface
of the flexible sheet 10C. Specifically, the central electrode 22C is
disposed so as to be superposed with the outermost peripheral end portion
32A of the second coil electrode 31C in plan view. In this way, a
capacitor is defined by the outermost peripheral end portion 32A of the
second coil electrode 31C, the central electrode 22C and the flexible
sheet 10C, the capacitor having a large opposing area and a comparatively
large capacitance.

[0102] The electrode pad 151A, which is arranged at a certain distance
from the outermost peripheral end portion 22A at which capacitive
coupling is possible, is located on the first main surface of the
flexible sheet 10C. In addition, the electrode pad 151B, which is
arranged at a certain distance from the central electrode 22C at which
capacitive coupling is possible, is located on the first main surface of
the flexible sheet 10C. In this way, a capacitor having a small
capacitance is preferably defined by the outermost peripheral end portion
22A and the electrode pad 151A, which are located on the same surface. In
addition, a capacitor having a small capacitance is preferably defined by
the central electrode 22C and the electrode pad 151B, which are located
on the same surface.

[0103] The wireless communication IC 80 is mounted on the flexible sheet
10C via the group of electrode pads, which includes the electrode pads
151A and 151B, arranged in a predetermined pattern.

[0104] With such a configuration, capacitive coupling obtained on the same
surface is much lower than capacitive coupling between opposing
electrodes. Therefore, the capacitance defined by the outermost
peripheral end portion 22A and the electrode pad 151A and the capacitance
defined by the central electrode 22C and the electrode pad 151B obtained
by capacitive coupling on the same surface are much smaller than that of
the capacitor formed of the innermost peripheral end portions 22B and 32B
and the capacitance defined by the outermost peripheral end portion 32A
and the central electrode 22C.

[0105] Therefore, the combined capacitance of the resonant circuit is
determined by the capacitance defined by the outermost peripheral end
portion 22A and the electrode pad 151A and the capacitance defined by the
central electrode 22C and the electrode pad 151B. As a result, as with
the first, second and third preferred embodiments of the present
invention, an antenna module can be provided that is not affected by
variations in the formation of the antenna 1C and has stable
communication characteristics.

[0106] Next, an antenna and an antenna module according to a fifth
preferred embodiment of the present invention will be described with
reference to the drawings. FIG. 9 is an exploded perspective view
illustrating the configuration of an antenna module 100D according to
this preferred embodiment of the present invention. FIG. 10 is a side
view of the antenna module 100D according to this preferred embodiment of
the present invention. The antenna module 100D according to this
preferred embodiment of the present invention preferably does not include
the flexible sheet 10 and the mounting substrate 15 of the antenna module
100 described in the first preferred embodiment of the present invention,
but instead includes an insulator substrate 10D, which has a
configuration in which insulator layers 10DA and 10DB are layered.

[0107] The insulator layer 10DA of the antenna module 100D corresponds to
the flexible sheet 10 of the antenna module 100 and the insulator layer
10DB of the antenna module 100D corresponds to a layer that forms the
mounting substrate 15 of the antenna module 100 with an area
substantially the same as that of the flexible sheet 10. Also with this
configuration, an antenna module that has stable communication
characteristics can be provided.

[0108] In the above description, the electrode pads 151A and 151B, which
are located on the mounting substrate 15 and the insulator layer 10DB,
are preferably used as electrodes to mount the wireless communication IC
80, but, in addition to the electrode pads 151A and 151B, a structure in
which electrodes to mount the wireless communication IC 80 are provided
and these electrodes are connected to each other with a wiring electrode
pattern may be adopted.

[0109] In addition, in the above-described preferred embodiments, cases
were described in which the wound line-shaped electrode portions of the
first and second coil electrodes including a flexible sheet or insulator
layer therebetween almost entirely do not oppose each other, whereas ends
of both the first coil electrode and the second coil electrode preferably
have a planar shape that is wider than the respective line-shaped
portions and oppose each other over substantially the entire areas
thereof. However, provided that the above-described predetermined
inductances and capacitances are obtained, the structure illustrated in
FIGS. 11A and 11B may be adopted. FIGS. 11A and 11B are plan views
illustrating another example of formation of a first coil electrode and a
second coil electrode. FIG. 11A illustrates a case in which inner
peripheral ends of the first coil electrode 21 and the second coil
electrode 31 do not have a wide planar shape and substantially oppose the
line-shaped electrode as they are. FIG. 11B illustrates a case in which
the inner peripheral ends of the first coil electrode 21 and the second
coil electrode 31 oppose each other while being shifted from each other
by a predetermined amount. The same functional effect as in each of the
above-described preferred embodiments can also be obtained with these
structures. In addition, although not illustrated, even if a
configuration in which both ends of the first coil electrode and the
second coil electrode do not have a wide planar shape is adopted, this
configuration can be applied to each of the preferred embodiments of the
present invention.

[0110] Furthermore, in the above descriptions, an example was described in
which a wireless communication IC chip is used as is, but an
electromagnetic coupling module such as that illustrated in FIGS. 12A and
12B may be used instead. FIGS. 12A and 12B illustrate a configuration of
an electromagnetic coupling module 90, where FIG. 12A illustrates an
external perspective view and FIG. 12B illustrates an exploded layered
view.

[0111] The electromagnetic coupling module 90 includes a power-feeding
substrate 91 and the wireless communication IC 80, which is mounted on
the power-feeding substrate 91, as illustrated in FIGS. 12A and 12B. The
power-feeding substrate 91 preferably includes a multilayer circuit board
formed by stacking dielectric layers, on which electrode patterns have
been formed on surfaces thereof, on top of one another. For example, as
illustrated in FIG. 12B, a structure is preferably used that is
preferably formed by stacking, for example, nine dielectric layers 911 to
919 on top of one another. On the dielectric layer 911, which is the
uppermost layer, mounting lands 941A and 941B for the wireless
communication IC 80 are formed and respective surface electrode patterns
951A and 951B are formed on the mounting lands 941A and 941B. On the
second to eighth dielectric layers 912 to 918, respective first C-shaped
pattern electrodes 922 to 928 and second C-shaped pattern electrodes 932
to 938 are formed.

[0112] The first C-shaped pattern electrodes 922 to 928 are electrically
connected to one another by via holes and define a first coil whose axial
direction is the stacking direction. The two ends of the first coil are
respectively connected to the mounting lands 941A and 941B provided on
the dielectric layer 911, which is the uppermost layer, through via
holes. In addition, the second C-shaped pattern electrodes 932 to 938 are
electrically connected to one another by via holes and define a second
coil whose axial direction is the stacking direction. The two ends of the
second coil are respectively connected to end portions of the surface
electrode patterns 951A and 951B provided on the dielectric layer 911,
which is the uppermost layer, through via holes.

[0113] Two outer connection electrodes 961 and 962 are located on the
dielectric layer 919, which is the lowermost layer. The two outer
connection electrodes 961 and 962 are respectively connected to the first
C-shaped pattern electrodes 922 to 928 and the second C-shaped pattern
electrodes 932 to 938 via through holes. These two outer connection
electrodes play the same role as the mounting lands to connect the
wireless communication IC to the outside, as described in each of the
above-described preferred embodiments.

[0114] While preferred embodiments of the present invention have been
described above, it is to be understood that variations and modifications
will be apparent to those skilled in the art without departing from the
scope and spirit of the present invention. The scope of the present
invention, therefore, is to be determined solely by the following claims.